Cylinder locks are well known in the art and typically include a cylinder plug rotatable within the bore of a shell, the plug having a longitudinal access opening therein for a key, and some form of mechanical stop means cooperating with the shell and plug preventing rotation of the plug unless a properly configured key is utilized to operate the mechanical stop means. Typically, the mechanical stop means would include tumblers which clear a shear line upon being raised by a properly bitted key. In addition to being properly bitted, a key must have a key blade cross section which fits into a keyway in the cylinder plug.
Quite often, for a number of different purposes, it is highly desirable to be able to quickly change the cross-sectional area of the keyway which, of course, determines the cross sectional area of the key blade and the blade of the keyblank. For example, in master keying a configuration can be devised where a master key could fit into all keyways of a system, but only certain individual keys could operate with certain keyways.
Additionally, in connection with a locksmith stocking locks having particular keyways and in production of locks having particular keyways, flexibility in providing keyways on demand would be highly desirable but at present is not known or available.
In the area of key control, particular keyways could be devised which could be limited to particular users or customers for locks.
Commonly, control procedures are utilized to the extent possible to prevent unauthorized duplication of keys. Medeco Security Locks, Inc. of Salem, Va., for example, provides key control by manufacturing cylinders which use keys that must be made on special key cutting machines, selling only to professional security industries, and pursuing unauthorized manufacture and distribution of restricted keyblanks.
There is a need in the art for providing key control with easily exchanged restrictive keyway sections, by providing a multiplicity of keyway configuration possibilities. If multiple keyway possibilities may be obtained by simple change in a lock, similar to having a removable plug, then security against unauthorized key duplication can be increased. Moreover, as noted above, a changeable keyway lock would also provide for expanded possibilities of master key systems, reduce locksmith stocking requirements and simplify production requirements.
Master key pinlocks are known in which the key has selective portions cut away, see Donovan U.S. Pat. No. 567,305.
There are also teachings in the prior art of utilizing a thin section within a cylinder lock to define a keyway, such section being removable, see for example Gray Re. U.S. Pat. No. 20,143. However, such inserts are perpendicular to key access and define the keyway only at a limited point or points. Similar teachings are found in Taylor U.S. Pat. No. 234,213 (slotted disks define keyway); Jannette U.S. Pat. No. 2,790,318 (accordion folded member defines keyway); Singer U.S. Pat. No. 3,736,780 (face of plug defines configuration for key access); Malminen et al. U.S. Pat. No. 4,127,996 (insert disks define keyway at limited points); Hill et al. U.S. Pat. No. 4,231,242 (pins project in the key slot for limited contact points); Steinbach U.S. Pat. No. 4,446,709 (plate inserted at the face of the cylinder plug); and Preddey U.S. Pat. No. 4,478,061 (removable piece fitted at front of plug).
It is also known in the prior art to construct a cylinder lock plug of separate half cylindrical elements which fit together and define a keyway, see e.g. Schwartz U.S. Pat. No. 3,429,154, Nolin U.S. Pat. No. 3,702,553, and Gater U.S. Pat. No. 4,472,953.
It is further known in the art to provide an insert requiring a notch in the bottom of a key to define a keyway, see for example Yulkowski U.S. Pat. No. 3,287,945 and Neale U.S. Pat. No. 3,824,818.
Johnstone, in U.S. Pat. No. 3,597,948, shows a keyway with a additional groove in the end of the key to increase the number of lock combinations, but the keyway is not changeable.
Even in the well worked prior art of cylinder locks, there remains a need in the art for a simple and effective construction to allow a cylinder lock plug to accommodate different key sections by providing a changeable keyway which extends the length of the plug and as a consequence also provides enhanced master keying possibilities.